1. Field of The Invention
The present invention relates to an injection control method and injection control device of a die-casting machine, which can be specifically used for injection control of a die-casting machine for manufacturing high-quality die-casting products without burr occurrence.
2. Description of Related Art
Conventionally, it is known that quality of die-casting molding products is largely affected by an injection speed and injection pressure in filling molten material into mold die. Especially, sufficient pressurization is required before the molten material solidifies and therefo re a die-casting machine having double-stage driving cylinder devices for injection and boost has been used.
Generally, in the die-casting machine of this type, an injection plunger advances at a low speed and the molten material is started to be filled into the mold cavity while avoiding the molten material from getting choppy. When an end of the molten material reaches a gate portion of the die and pressure of filling injection cylinder device increases, the injection plunger is advanced at a high speed for avoiding the temperature of the molten material from being lowered to fill the mold cavity with the molten material rapidly.
In succession to the injection process, when the molten material is filled into the mold-die to further raise the pressure of the injection cylinder device or when the injection plunger reaches a predetermined position corresponding to completion of filling, high pressure is applied to a boost cylinder device to conduct boosting process for increasing pressurizing force of the injection pressure in the mold die.
Specific arrangement of the conventional double-stage cylinder type die-casting machine will be described below.
In FIG. 6, molten material 92 to be filled in the mold cavity 91 is supplied to injection sleeve 93 of a die-casting machine 90. An injection plunger 94 is driven by a filling injection cylinder device 95 to inject the molten material 92. After completing filling process, hydraulic oil at a backside of the injection cylinder device 95 is pressurized by boost cylinder device 96 with a large diameter to a high pressure to boost the molten material 92 filled in the mold cavity 91 through the injection cylinder device 95.
Injection speed level CV and injection pressure level CP during injection process and boosting process in the die-casting machine are shown in Fig. 7. In the figure, the injection cylinder device 95 advances initially at a low speed VL and fills the molten material rapidly at a high speed VH from time point t1 which is braked by virtue of filling pressure of the molten material 92 in accordance with completion of filling process. The boost cylinder 96 is actuated at time point t2 to pressurize the molten material 92 so that the molten material 92 in the mold cavity 91 reaches pressure PH. The injection cylinder 95 is further advanced and is stopped at time point t3 when solidification of the molten material is completed.
For linking control of the injection cylinder device 95 and the boost cylinder device 96 (switching process from the injection process and the boosting process), sequence-valve method for detecting injection pressure fluctuation to conduct switch and limit-switch method for detecting the advancing position of the injection plunger have been used.
Following hydraulic circuit is used in the above sequence valve method.
In FIG. 8, an injection hydraulic circuit 114 from a check valve 111 and injection speed control valve 112 to an accumulator 113 is connected to the injection cylinder device 95. On the other hand, a boost hydraulic circuit 117 reaching the accumulator 113 through a pilot operation boost control valve 116 to be opened and shut by a sequence valve 115.
The sequence valve 115 opens the boost control valve 116 when the pressure of the injection hydraulic circuit 114 exceeds a predetermined boost initiation pressure. Accordingly, when advancement of the injection cylinder device 95 is started by operating the injection speed control valve 112 for conducting the injection process and filling pressure is increased in accordance with completion of filling molten material into the mold die to reach the predetermined boost initiation pressure, the sequence valve 115 is actuated to open the boost control valve 116 to start advancement of the boost cylinder device 96, thereby conducting boosting process.
As shown in FIG. 9, the injection cylinder device 95 has an injection piston 95A, which is advanced by hydraulic pressure of hydraulic oil supplied to a backside thereof by the injection hydraulic circuit 114. Flow-rate of the hydraulic oil from the injection hydraulic circuit 114 is controlled by the injection speed control valve 112 to switch advancement and suspension of the injection piston 95A and adjust advancing speed thereof.
The boost cylinder device 96 has a boost piston 96A thereinside, which is advanced by hydraulic pressure of the hydraulic oil supplied to a backside thereof from the boost hydraulic circuit 117 to pressurize the injection piston 95A from backside through an intermediate member 95B of the injection cylinder device 95. The flow of the hydraulic oil from the boost hydraulic circuit 117 is controlled by the boost control valve 116, which switches advancement and suspension of the boost piston 96A.
On-off operation of the boost control valve 116 is conducted by the sequence valve 115. An electrovalve or the like for switching in response to filling pressure by an appropriate means is suitably used for the sequence valve 115.
Incidentally, in the above-described double-stage die-casting machine, the flow-rate of the hydraulic oil given to the boost cylinder device stays constant without being variably controlled in the boosting process for boosting the injection cylinder device by the boost cylinder device. This is because on-off operation of the hydraulic oil is conducted by the boost control valve and an on-off two-position switching type constant flow valve is conventionally used for the boost control valve.
Since the hydraulic oil is supplied at a constant flow-rate to the boost cylinder device, boost characteristics of casting pressure becomes the injection pressure level CP shown in FIG. 7, in which increase curve is represented as a quadratic curve being less gradient as approaching to maximum pressure PH. This is because the injection plunger receives much resistance in accordance with solidification of the molten material in the mold die and the boost is blunted. More specifically, the casting pressure P is in proportion to square root of product of elapsed time t and parameter a.
On the other hand, burr critical boost curve is known in boosting process. The burr is generated when an excessive pressure is applied to the mold die in boosting process etc. to leak the molten material from parting surface of the mold die. The burr critical boost curve is given as a curve CX where the casting pressure P is in proportion to a product of square of elapsed time t and parameter a (see FIG. 7).
The burr critical boost curve CX becomes such quadratic curve because the molten material in the mold die is not solidified at the initial stage of boosting process and fluidity of the molten material is high enough to leak the molten material from the parting surface, which prevents high pressure from being applied. On the other hand, when the molten material is solidified in accordance with elapsed time, the leakage to the parting line is hard to be caused, so the burr is not likely to be generated when high pressure is applied.
However, in the conventional die-casting machine where the hydraulic oil is supplied to the boost cylinder device at a constant flow-rate, the boost characteristic of the casting pressure is difficult to be approximated to the burr critical boost curve, so that burrs are frequently generated in conducting high-speed casting or using a mold die having low parting surface accuracy, which makes it impossible to manufacture die-casting products with high-quality.
An object of the present invention is to provide a injection control method and device of a die-casting machine for manufacturing high-quality die-casting products without burrs even in high-speed casting and mold die of low accuracy.
To achieve the above object, after filling the molten material into the cavity by advancing the injection piston, the pressure is controlled in accordance with a predetermined selective boost curve set along a burr critical boost curve for avoiding burr occurrence in the casting die during boosting process by the boost cylinder device in the present invention. More specifically, the present invention is arranged as follows:
A method according to the present invention is an injection control method of a boost-type die-casting machine including an injection plunger for injecting molten material into a casting die, an injection cylinder device having an injection piston for driving the injection plunger, and a boost cylinder device for boosting hydraulic oil supplied to the injection cylinder device. The method is characterized in including the steps of: providing a flow-rate control valve capable of continuously regulating flow-rate of hydraulic oil discharging channel of the injection cylinder device; and, during boosting process by the boost cylinder device, synchronously controlling back-pressure of the injection cylinder device and back-pressure of the boost cylinder device.
A device according to the present invention is an injection control device of a boost-type die-casting machine having an injection plunger for injecting molten material to a casting die, an injection cylinder device having an injection piston for driving the injection plunger, and a boost cylinder device having a boost cylinder for boosting hydraulic oil supplied to the injection cylinder device. The device is characterized in further having; a flow-rate control valve capable of continuously controlling a flow-rate in a hydraulic discharging channel of the injection cylinder device; and a synchronous controller for synchronously controlling a back-pressure of the injection cylinder device and a back-pressure of the boost cylinder device during boosting process by the boost cylinder device.
According to the above arrangement, since the flow-rate in the hydraulic oil discharging channel is continuously controlled by the flow-rate control valve to set the flow-rate variable, boost characteristic can be adjusted to correspond to the burr critical boost curve, thereby preventing generating burr in advance. Accordingly, high-quality die-casting products without burr can be manufactured even in high-speed casting or using low-accuracy mold die. Further, since both of the back-pressures of the injection cylinder and the boost cylinder, the size of the device can be reduced.
Incidentally, either one of open-control and real-time feedback control can be preferably used for the control method.
In the method of the present invention, the flow-rate control valve is preferably controlled so that a relationship between casting pressure and boost time in the casting die is changed in accordance with a selective curve along a predetermined critical boost curve for avoiding burr occurrence to the casting die during the synchronous controlling process.
In the device of the present invention, the synchronous controller preferably controls the flow-rate control valve so that a relationship between a casting pressure and boost time of the casting die changes in accordance with a selective curve along a predetermined critical boost curve for avoiding burr occurrence to the casting die during the synchronous controlling process.
In the above arrangement, since the boosting process is conducted by a flow-rate control valve composed of a high-responsive electrohydraulic servovalve using a controller along a predetermined critical curve not causing the burr, the burr can be prevented from generating, thus manufacturing high-quality die-casting products without burr even in high-speed casting or using low accuracy mold die. Further, since the high-responsive electrohydraulic servovalve is used, responsivity and accuracy can be improved.
In the method of the present invention, the flow-rate control valve is preferably controlled by comparing a detected pressure value detected by the injection cylinder device and the boost cylinder device and a command pressure value for every elapsed time given in accordance with a predetermined program to eliminate difference between the pressure values.
In the device of the present invention, the synchronous controller preferably compares a detected pressure value detected by the injection cylinder device and the boost cylinder device and a command pressure value for every elapsed time given in accordance with a predetermined program and controls the flow-rate control valve to eliminate difference between the pressure values.
According to the above arrangement, since the control is conducted along the predetermined critical curve not causing the burr, the burr generation can be prevented in advance, thereby manufacturing high-quality die-casting products without burr even in high-speed casting process or using low-accuracy mold die.
In the method according to the present invention, the flow-rate control valve is preferably controlled by comparing difference between the detected pressure value and the command pressure value and open-degree of the flow-rate control valve so that the open-degree corresponds to the difference.
In the device according to the present invention, the synchronous controller preferably compares difference between the detected pressure value and the command pressure value and open-degree of the flow-rate control valve and controls the flow-rate control valve so that the open-degree corresponds to the difference.
According to the above arrangement, responsivity of open-degree control and accuracy of the flow-rate control valve can be improved.
In the device-according to the present invention, the flow-rate control valve may preferably be a high-responsive electrohydraulic servovalve.
According to the above arrangement, the responsivity and accuracy of the flow-rate control valve can be improved.
In the device of the present invention, the hydraulic discharging channel of the injection cylinder device and a hydraulic discharging channel from the boost cylinder device are preferably connected.
According to the above arrangement, since back-pressure side of the injection cylinder device and the boost cylinder device are interconnected for synchronization and both of the back-pressures of the injection cylinder and the boost cylinder can be controlled, the size of the device can be reduced.
In the device according to the present invention, the flow control valve preferably has a main spool to be opened and shut by a pilot servovalve.
According to the above arrangement, the open-degree can be more accurately and easily controlled by the main spool.
In the above, a position sensor for detecting open-degree of the main spool may preferably be provided.
According to the above arrangement, the open-degree of the main spool can be accurately and easily conducted.
A command signal outputted by the position sensor and a difference between a command pressure value outputted by a boost controller and a detected pressure value detected by the injection cylinder device and the boost cylinder device are preferably fed back to an input of the pilot servovalve.
According to the above arrangement, responsivity and accuracy of the open-degree control of the main spool can be improved.
In the device according to the present invention, the synchronous controller may further have a pressure detector for detecting a casting pressure of the injection cylinder device, a pressure processor for processing an output from the pressure detecting means, a boost controller for outputting a command pressure value for every elapsed time according to a predetermined program, and a comparator for calculating a difference between a pressure outputted by the pressure processing means and a command pressure value outputted by the boost controller.
And, the synchronous controller may further have a servo amplifier for controlling the flow-rate control valve so that a relationship between a casting pressure and boost time of the casting die changes in accordance with a selective curve along a predetermined critical boost curve for avoiding burr occurrence to the casting die during the boosting process by the boost cylinder device based on a difference outputted by the comparator.
According to the above arrangement, since the boosting process is conducted along a predetermined critical curve without generating burr, the burr generation can be prevented in advance, thereby high-quality die-casting products without burr can be produced even in high-speed casting process or by using a mold die with low-accuracy.
In the device of the present invention, a boost control valve for controlling boosting time may preferably provided on a hydraulic oil supply side of the boost cylinder.
In the above arrangement, the boost control valve may have a spool movable by operating a switching valve and an adjusting stopper for adjusting a moving amount of the spool, a distal end portion of the hydraulic oil supply side of the spool being tapered for narrowing the flow-rate of the hydraulic oil to regulate pressure and flow-rate of pressurizing portion of the boost piston.
According to the above arrangement, since the spool of the boost control valve is configured in a shape capable of narrowing the flow-rate of the hydraulic oil, even when a trouble disabling the function of the flow-rate control valve is occurred, the open-degree of the spool can be adjusted to be small using the adjusting stopper to set a spool open-degree position capable of obtaining predetermined boost curve. Accordingly, normal boosting process can be temporarily secured.